Although the molecular basis for obesity is largely unknown, the identification of the “OB gene” and protein encoded (“OB protein” or “leptin”) has shed some light on mechanisms the body uses to regulate body fat deposition. See, PCT publication, WO 96/05309 (Dec. 22, 1996), Friedman et al.; Zhang et al., Nature 372: 425–432 (1994); see also, the Correction at Nature 374: 479 (1995). The OB protein is active in vivo in both ob/ob mutant mice (mice obese due to a defect in the production of the OB gene product) as well as in normal, wild type mice. The biological activity manifests itself in, among other things, weight loss. See generally, Barrinaga, “Obese” Protein Slims Mice, Science 269: 475–456 (1995). The OB protein, derivatives and use thereof as modulators for the control of weight and adiposity of animals, including mammals and humans, has been disclosed in greater detail in PCT publication WO 96/05309 (Dec. 22, 1996), hereby incorporated by reference, including figures.
The other biological effects of OB protein are not well characterized. It is known, for instance, that in ob/ob mutant mice, administration of OB protein results in a decrease in serum insulin levels, and serum glucose levels. It is also known that administration of OB protein results in a decrease in body fat. This was observed in both ob/ob mutant mice, as well as non-obese normal mice Pelleymounter et al., Science 269: 540–543 (1995); Halaas et al., Science 269: 543–546 (1995). See also, Campfield et al., Science 269: 546–549 (1995) (Peripheral and central administration of microgram doses of OB protein reduced food intake and body weight of ob/ob and diet-induced obese mice but not in db/db obese mice.) In none of these reports have toxicity's been observed, even at the highest doses.
Despite the promise of clinical application of the OB protein, the mode of action of the OB protein in vivo is not clearly elucidated. Information on the OB receptor, shows high affinity binding of the OB protein detected in the rat hypothalamus, which indicates OB receptor location. Stephens et al., Nature 377: 530–532. The db/db mouse displays the identical phenotype as the ob/ob mouse, i.e., extreme obesity and Type II diabetes; this phenotype is thought to be due to a defective OB receptor, particularly since db/db mice fail to respond to OB protein administration. See Stephens et al., supra.
With the advances in recombinant DNA technologies, the availability of recombinant proteins for therapeutic use has engendered advances in protein formulation and chemical modification. One goal of such modification is protein protection and decreased degradation. Fusion proteins and chemical attachment may effectively block a proteolytic enzyme from physical contact with the protein backbone itself, and thus prevent degradation. Additional advantages include, under certain circumstances, increasing the stability, circulation time, and the biological activity of the therapeutic protein. A review article describing protein modification and fusion proteins is Francis, Focus on Growth Factors 3: 4–10 (May 1992) (published by Mediscript, Mountview Court, Friern Barnet Lane, London N20, OLD, UK).
One such modification is the use of the Fc region of immunoglobulins. Antibodies comprise two functionally independent parts, a variable domain known as “Fab”, which binds antigen, and a constant domain, known as “Fc” which provides the link to effector functions such as complement or phagocytic cells. The Fc portion of an immunoglobulin has a long plasma half-life, whereas the Fab is short-lived. Capon, et al., Nature 337: 525–531 (1989).
Therapeutic protein products have been constructed using the Fc domain to provide longer half-life or to incorporate functions such as Fc receptor binding, protein A binding, complement fixation and placental transfer which all reside in the Fc proteins of immunoglobulins. Id. For example, the Fc region of an IgG1 antibody has been fused to the N-terminal end of CD30-L, a molecule which binds CD30 receptors expressed on Hodgkin's Disease tumor cells, anaplastic lymphoma cells, T-cell leukemia cells and other malignant cell types. See, U.S. Pat. No. 5,480,981. IL-10, an anti-inflammatory and antirejection agent has been fused to murine Fcγ2a in order to increase the cytokine's short circulating half-life. Zheng, X. et al., The Journal of Immunology, 154: 5590–5600 (1995). Studies have also evaluated the use of tumor necrosis factor receptor linked with the Fc protein of human IgG1 to treat patients with septic shock. Fisher, C. et al., N. Engl. J. Med., 334: 1697–1702 (1996); Van Zee, K. et al., The Journal of Immunology, 156: 2221–2230 (1996). Fc has also been fused with CD4 receptor to produce a therapeutic protein for treatment of AIDS. See, Capon et al., Nature, 337: 525–531 (1989). In addition, the N-terminus of interleukin 2 has also been fused to the Fc portion of IgG1 or IgG3 to overcome the short half life of interleukin 2 and its systemic toxicity. See, Harvill et al., Immunotechnology, 1: 95–105 (1995).
Due to the identification of the OB protein as a promising therapeutic protein, there exists a need to develop OB analog compositions for clinical application in conjunction with or in place of OB protein administration. Such development would include OB analog compositions where protein formulations and chemical modifications achieve decreased protein degradation, increased stability and circulation time. The present invention provides such compositions.